Spherical reflective screen with focus and method for manufacturing the same

ABSTRACT

Disclosed are a spherical reflective screen for displaying an image and a method for manufacturing the screen. The screen has a spherical surface with a radius of curvature of a circle drawn centering around a point, and a focal length of the screen is the same as a projection length of a projector so that the projector is located at a focal point of the screen, thus allowing the image formed by means of light projected from the projector to be straightly reflected on the screen but ambient light to be diffused to the outside. A frictional surface and diffusing lines are simultaneously formed on an aluminum foil by rubbing the double-layered aluminum foils together in one direction, therefore, viewing angle and resolution of the screen are improved two times or more.

TECHNICAL FIELD

The present invention relates to a screen for displaying an image with ahigh luminance and a reflectivity of more than 10%, ten times as much asthe reflectivity (i.e., 1%) of a conventional screen, and moreparticularly to a screen for displaying, which directs toward theviewers only light (image) projected from a projector disposed at afocal point of the screen and reflects off-axis light and defusesambient light so that 10 times higher luminance is performed on thescreen. The surface material of screen of the present invention consistsof double-layered aluminum foil, on which friction face and diffusionlines are formed along the scanning lines. From rubbing the material'sfriction and diffusion face, the screen of the present invention gets10-45% reflectivity so that it performs 10-45 times brighter and 2 timeshigher diffusion effect than the conventional screen. The screen of thepresent invention has improved as well 2 times or more in viewing angleand 10-20 times in resolution. Also, this invention relates to a methodof manufacturing the screen.

BACKGROUND ART

As shown in FIG. 1, a conventional diffusion type plane diffusing screen10 is configured such that light incident on the screen 10 is diffusedin all directions. An image formed on the screen 10 is even, but has areflectivity of 1% (generally, referred to as “1 gain”), thus beingdark. Since the light incident on the screen 10 is diffused in alldirections, the screen 10 acts on light from all directions.Accordingly, the screen 10 has a reduced resolution due to ambient lightfrom all directions.

As shown in FIG. 2, a plane reflective screen 20 with an improvedsurface reflectivity is configured such that light projected from aprojector is incident on the screen 20 at an incident angle (∠A) andthen reflected from the screen 20 at a reflection angle (∠B) same as theincident angle (∠A), thus allowing a viewer to watch an image formed onthe screen 2 in the range of C obtained by the reverse angle of thereflection angle (∠B).

That is, a hot spot is formed in the range of C. As shown in FIG. 2, theimage displayed on the screen 2 is bright only at a central portion, butis dark at other peripheral portions, thus being invisible at theperipheral portions. In case that the surface reflectivity of the screen2 is increased, the hot spot become brighter. On the other hand, in casethat the surface reflectivity of the screen 2 is decreased, the hot spotwill becomes darker and enlarger.

Further, in case that the surface reflectivity of the screen 2 is high,a screen having a non-spherical shape cannot display an image with evenluminance, thus displaying uneven spots thereon. Further, since thescreen having a non-spherical shape does not form an exact focus, thisnon-spherical screen cannot be used in a device requiring a highluminance.

However, all spherical screens cannot increase the luminance of screens.Only when a spherical screen comprises an optical element such as lensand a reflective surface, a screen can obtain an image with evenluminance and high reflectivity over the whole surface of the screen.

Accordingly, there is required a method for forming an opticalconstitution and a surface reflectivity suitable for the structure ofthe screen.

Further, since the luminance of a screen is inversely proportional tothe viewing angle of a screen, when a screen displays an image with ahigh luminance, the viewing angle of the screen is narrowed. The screenwith the narrowed viewing angle cannot be effectively operated.Accordingly, there is required a spherical screen, which can display animage with a high luminance at a wider viewing angle.

DISCLOSURE OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide aspherical reflective screen, which displays an image having a even andhigh luminance with an improved reflectivity so that the viewing angleand resolution of the screen are improved more than two times, and amethod for manufacturing the spherical reflective screen.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a sphericalreflective screen for displaying an image, comprising:

-   -   a spherical surface with a radius of curvature of a circle drawn        centering around a point, and including a frictional surface and        diffusing lines formed on one side of an aluminum foil by        rubbing the aluminum foil,    -   wherein a projector is located at a focal point of the spherical        surface so that the screen displays an image with a high        luminance and an improved resolution at an improved viewing        angle.

In accordance with another aspect of the present invention, there isprovided a method for manufacturing a spherical reflective screen fordisplaying an image,

-   -   wherein a frictional surface and diffusing lines are formed on        aluminum foil by rubbing two aluminum foils together in a        longitudinal or lateral direction, and the aluminum foil        provided with the frictional surface and the diffusing lines is        bent so that the aluminum foil provided with the frictional        surface and the diffusing lines has a designated radius of        curvature and serves as the spherical surface of the screen.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view of conventional plane diffusion screen;

FIG. 2 is a schematic view illustrating a hot-spot phenomenon occurringon a plane reflective screen;

FIGS. 3 a to 3 c are schematic views of a spherical mirror, and morespecifically:

FIG. 3 a is a schematic view of the spherical mirror onto which light ata position outside the range of a focus is projected;

FIG. 3 b is a schematic view of the spherical mirror onto which light inthe range of the focus is projected; and

FIG. 3 c is a schematic view of the spherical mirror onto which light ata position inside the range of the focus is projected;

FIG. 4 is a schematic view of a reflective screen in accordance with thepresent invention;

FIG. 5 is a schematic view illustrating diffusing lines of thereflective screen in accordance with the present invention;

FIG. 6 is a schematic view illustrating a process for forming adiffusing lines and a frictional surface on the reflective screen inaccordance with the present invention;

FIG. 7 is a schematic view illustrating a method for manufacturing aspherical frame;

FIG. 8 is a schematic view illustrating a step of forming the sphericalshape of an aluminum foil during a process for manufacturing thereflective screen in accordance with the present invention;

FIG. 9 is a schematic view illustrating a method for manufacturing thereflective screen in accordance with the present invention;

FIG. 10 is an enlarged photograph of an aluminum foil obtained by thepresent invention, as seen through a microscope;

FIG. 11 is an enlarged photograph of a conventional aluminum foil, asseen through a microscope;

FIG. 12 is a photograph illustrating the resolution of a sphericalscreen with diffusing lines formed thereon; and

FIG. 13 is a photograph illustrating the resolution of a sphericalscreen without diffusing lines.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, preferred embodiments of the present invention will be described indetail with reference to the annexed drawings.

As shown in FIGS. 4 and 5, a spherical screen 1 of the present inventioncomprises a reflective surface having a spherical shape (R) with aradius of curvature (R1) of a circle drawn centering around a point(R2).

The reflective surface of the screen 1 has a reflectivity of 10% at theminimum to 45% at the maximum, and preferably 10% to 30%. However, thereflective surface of the screen 1 is not limited thereto.

In case that the reflectivity of the reflective surface of the screen 1is less than 10%, the screen 1 cannot obtain a desirably high luminance.On the other hand, in case that the reflectivity of the reflectivesurface of the screen 1 is more than 45%, it is difficult to perform thefollowing procedure for forming diffusing lines 6 and a frictionalsurface 5 on an aluminum foil. That is, the reflectivity of thereflective surface of the screen is limited in the range of 10% to 45%.Here, the reflectivity of 10% to 45% means that a screen luminance indexis 10 to 45 gain.

A focal point (F) is formed at a central point of the radius ofcurvature from the point (R2) to the reflective surface of the sphericalscreen 1. A distance from the focal point (F) to the reflective surfaceof the spherical screen 1 is referred to as a focal length.

A projector 7 is located at the focal point (F).

A projection length (F1) of the projector 7 is the same as the focallength of the screen 1.

As shown in FIG. 3 b, light from the projector 7 located at the focalpoint (F), which is incident on the spherical surface (R), is straightlyreflected on the spherical surface (R). Then, a viewer can watch aformed image in the range of C1 obtained by the inverse angle of thereflection angle.

As shown in FIG. 3 c, light from the projector 7 located in the front ofthe focal point (F), which is incident on the spherical surface (R), isreflected on the spherical surface (R) at an increased angle, thuscausing a hot spot phenomenon.

As shown in FIG. 3 a, light from the projector 7 located in the rear ofthe focal point (F), which is incident on the spherical surface (R), isreflected toward the focal point (F), thus causing the visual angle (A)to be narrowed.

The above-described cases relate to a spherical mirror with areflectivity of 100%. The screen of the present invention has adesignated reflectivity and diffusing coefficient. In order to obtainoptimized effects of improved viewing angle and resolution, since thehot spot is generated in proportion to the diffusing coefficient, thefocal length from the focal point (F) to the reflective surface of thescreen must be the same as the projection length (F1).

As shown in FIGS. 4 and 6, the reflective surface of the sphericalscreen 1 includes a frictional surface 5 with a designated reflectivityand a plurality of diffusing lines 6 arranged in a lateral directionformed by rubbing two aluminum foils 3 together. The diffusing lines 6serve as diffusing surfaces. Then, a protective surface 2 is formed onthe inner sides of the frictional surface 5 and the diffusing lines 6,and a supporting plate 4 made of plastic is attached to outer sides ofthe frictional surface 5 and the diffusing lines 6.

Here, the protective surface 2 is formed by coating silicon or acrylicresin on the inner side of the frictional surface 5 and diffusing lines6. Silicon or acrylic resin is not an obstacle to the light projectionof the projector 7.

The protective surface 2 of FIG. 6 maybe formed by attaching a thinsheet made of Teflon to the outer sides of the frictional surface 5 andthe diffusing lines 6.

Teflon is not easily contaminated by external dust, has a high hardnessand a high resistivity to foreign substances, thus forming a solidscreen surface. Further, fine laterally curved lines are formed on thescreen surface in a longitudinal direction and then laterallyoverlapped, thus remarkably increasing the visual angle of the screen.

The screen of the present invention is characterized in that thediffusing lines 6 are formed on the screen so as to obtain the desiredviewing angle of the screen and the frictional surface 5 is formed onthe screen so as to obtain the desired reflectivity.

Hereinafter, a method for manufacturing the above-described surface ofthe aluminum foil 3 provided with the diffusing lines 6 and thefrictional surface 5 will be described in detail.

That is, the diffusing lines 6 and the frictional surface 5 are formedon the aluminum foils 3 and 3A by rubbing left and right aluminum foils3 and 3A against each other and by transferring the left and rightaluminum foils 3 and 3A between left and right upper rollers 9 and 9Aand between left and right lower rollers 11 and 11A in rolling thealuminum foils 3 and 3A. Here, the diffusing lines 6 are formed on thealuminum foils 3 and 3A in the direction of the applied friction so thatthe frictional surface 5 can have a reflectivity of 10% to 45% byadjusting pressure applied by left and right pressure rollers 10 and10A.

That is, the frictional surface 5 with a reflectivity of 10% to 45%shown in FIG. 10 is obtained by adjusting the pressure applied by theleft and right pressure rollers 10 and 10A.

In case that the reflectivity of the frictional surface 5 is less than10%, the screen cannot have high luminance efficiency. On the otherhand, in case that the reflectivity of the frictional surface 5 is morethan 45%, the depths of the scattering lines 5 and the frictionalsurface 5 are reduced in the above rubbing procedure.

FIG. 10 is a photograph of the frictional surface 5 with a reflectivityof 25% obtained by rubbing the aluminum foil 3 with a thickness of20-100 micron, preferably 50 micron by the above-described procedure,which is enlarged hundred times using a monitor microscope. Here, thediffusing lines 6 with a thickness of 10 micron are overlapped, thusallowing the screen provided with the frictional surface 5 and thediffusing lines 6 to have a viewing angle of 60°.

FIG. 11 is a photograph of the aluminum foil 3 obtained by aconventional rolling procedure without the use of the above rubbingprocedure. Here, the aluminum foil 3 does not have scattering lines.

Such an aluminum foil 3 obtained by the conventional rolling procedurehas a reflectivity 25% as same as that of the frictional surface, buthas a viewing angle of less than of 30°. Accordingly, it is difficult topractically use the aluminum foil 3 without diffusing lines as amaterial of the screen 2.

For reference, light was projected onto the reflection surface of thescreen of the present invention using a projector made by SANYO in Japan(Model No. plc-xp 41k), and the luminance of the screen was measured bya luminance measuring apparatus made by MINOLTA in Japan (Model No.LS-110).

Hereinafter, a method for manufacturing the aluminum foil provided withthe above-described diffusing lines 6 and frictional surface 5 will bedescribed in detail.

As shown in FIG. 7, an abrasive compound 33 is supplied onto one surfaceof a member having a desired radius of curvature (R) required by thespherical screen 1, and then the surface of the member is polished usinga rotating abrasive plate 31 with the radius of curvature (R). Thereby,a spherical frame 33 with the radius of curvature (R) is obtained.

As shown in FIG. 8, one surface of the aluminum foil 3 is pressed ontosuch a spherical frame 33, thus allowing the aluminum foil 3 to have theradius of curvature (R).

As shown in FIG. 9, the support plate 4 made of plastic is attached tothe other surface of the aluminum foil 38 with the radius of curvature(R). Thereby, the spherical screen 1 is completely manufactured.

As shown in FIG. 4, the spherical surface (R) of the screen 1 has theradius of curvature (R1) of a circle drawn centering around the point(R2), thus allowing the screen 1 to have proper optical characteristicsand reflectivity and locating the focal point (F) at a proper position.

The relation between the focal length (F′) and the length (R′) of thespherical surface (R) is represented by an equation of F′=R′/2.

Further, the relation between the projection length (F1) of theprojector 7 and the focal length (F′) is represented by an equation ofF1=F′.

More specifically, for example, in case that the screen 1 has the sizeof 100″, the projection length (F1) of the projector 7 is generally 4.5m.

In this case, since the relation between the projection length (F1) ofthe projector 7 and the focal length (F′) is represented by the aboveequation of F1=F′, the projector 7 is separated from the screen 1 by thedistance of 4.5 m. Then, since the relation between the focal length(F′) and the length (R′) of the spherical surface (R) is represented bythe above equation of F′=R′/2, i.e., R′=2F′, the length (R′) of thespherical surface (R) is 9 m.

Since the diffusing lines 6 shown in FIG. 6 are laterally formed on thefrictional surface 5, the lateral diffusing rate of light on the screen1 is two times as high as the longitudinal diffusing rate of light onthe screen 1.

Accordingly, compared to the conventional screen, it is possible toincrease the viewing angle of the screen 1 two times or more as broad asthe longitudinal viewing angle of the screen 1.

The above light diffusing removes the occurrence of a hot spot due tothe straight reflection shown in FIG. 4, thus allowing the screen 1 todisplay an image with a uniform luminance and increasing the viewingangle of the screen 1. The viewing angle is an essential factor requiredin the screen 1.

The spherical screen 1 of the present invention is configured so thatthe screen 1 receives light projected only from the projector 7 locatedat the focal point (F), and then displays an image using the receivedlight via the whole surface of the screen 1, but diffuses other externalinterfering light to the outside. Accordingly, the image displayed onthe screen 1 is not influenced by external interfering light even in abright space. Further, as a result of a test using a contrast patternrepresented by the diffusing lines 6, the resolution of the imagedisplayed by the screen 1 of the present invention is improved to twotimes as much as that of the conventional screen.

For example, as shown in FIG. 12, the spherical screen 1 provided withthe diffusing lines 6 has a high resolution so that even a letter in thesize of a 4-point in an image displayed on the screen 1 isdistinguishable. On the other hand, as shown in FIG. 13, theconventional spherical screen without diffusing lines has a relativelylow resolution so that a letter to the size of a 10-point in an imagedisplayed on the screen is distinguishable.

Accordingly, the resolution of the spherical screen 1 of the presentinvention provided with the diffusing lines 6 is improved more than twotimes as much as that of the conventional screen.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the present invention provides aspherical reflective screen, which displays an image having a highluminance with a reflectivity of 10% to 45% and forms an image by meansof only light projected from the projector located at the focal point ofthe spherical surface of the screen, thus enlarging the viewing angle ofthe screen more than two times via the fine diffusing lines laterallyformed on the screen and improving the resolution more than two timesvia the contrast pattern represented by the diffusing lines.

Further, the present invention provides a method for manufacturing aspherical reflective screen with improved viewing angle and resolution,which displays an image with a high luminance by forming a frictionalsurface and diffusing lines on an aluminum foil obtained by rubbing twoaluminum foils together, so that the luminance obtained due to thereflectivity of the surface of the screen, and the lateral viewing angleand the resolution of the screen obtained due to the diffusing lines areimproved, and by bending the aluminum foil provided with the frictionalsurface and the diffusing lines so that the aluminum foil provided withthe frictional surface and the diffusing lines has a designated radiusof curvature and serves as the spherical surface of the screen.

The screen of the present invention may be widely and effectively usedas an educational screen for providing a clear image with a highresolution in a bright classroom, a conference screen for providing aclear image in a bright office room without the use of a curtain, and anadvertising screen in a bright public place.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. (canceled)
 2. (canceled)
 3. A method for manufacturing the sphericalreflective screen for displaying an image, wherein the frictionalsurface and the diffusing lines are formed on the aluminum foil byrolling or rubbing the double-layered aluminum foils together in alongitudinal or lateral direction, and the aluminum foil provided withthe frictional surface and the diffusing lines is bent so that thealuminum foil provided with the frictional surface and the diffusinglines has a designated radius of curvature and serves as the sphericalsurface of the screen.
 4. (canceled)
 5. (canceled)
 6. A sphericalreflective screen for displaying an image as set forth in claim 3,wherein the spherical surface of the screen includes a protectivesurface made of silicon, acrylic resin or thin Teflon sheet attached tothe surface of the aluminum foil.